Probably the most rare 1st gen. performance option was RPO MA6 Heavy Duty Dual Disc Clutch. Offered only in '69, Chevrolet's comment about it was "The dual-disc system is well suited for extremely heavy-duty use on strip or track, including road racing. Also suitable for street use creating a new driving experience.". While it was available for all high performance applications, it was an ideal option for the Z/28.
Clyde